As integrated circuits continue to scale downward in size, the finFET (fin field effect transistor) is becoming an attractive device for use with modern semiconductor devices. In a finFET, the channel is formed by a semiconductor vertical fin (as compared with a planar channel in a conventional CMOS), and a gate electrode is located and wrapped around the vertical fin. FinFETs are commonly formed using one of two structure types of substrate. A bulk structure is one where the fins are formed in the bulk semiconductor substrate, with a gate formed above the bulk substrate. A silicon-on-insulator (SOI) structure is one where fins are formed in a thin semiconductor layer that sits on an insulator layer disposed on the bulk substrate (i.e. Si-on-oxide, or SOI substrate), with the gate formed over the thin semiconductor layer. Each structure type has various advantages and disadvantages.